Typical commercially available tire pressure monitoring system units are mounted to the inside of a tire in a position from which the air pressure within the tire cavity may be measured. Data representing pressure within the tire is then communicated by a transmitted signal to a reader external to the tire. For example, certain available units integrate a pressure sensing module with the valve stem of a tire. Electronics within the sensor unit measure the air pressure at the valve stem and transmit an appropriate signal to an external receiver. The receiver may be located proximally located to the sensor unit or in a remote location such as the passenger compartment.
While working well, such systems are not useful in meeting the industry's needs in certain applications. For example, in some applications such as in NASCAR race tires, there is a need for a tire pressure-measuring device that may be used conveniently in a two tire system by officials to check start inflation pressure. Such a system should functionally measure inflation pressure without requiring an official to touch the tire. A suitable pressure measuring system will give a positive indication of specific tire read and, for competition reasons, preclude one team from reading another team's tire information. In addition, the pressure measuring system and device must be capable of validation with a mechanical pressure gauge if necessary. In such applications, the tire pressure measuring device should be hardy and capable of surviving multiple races. Ideally, the device will be a standard supported component of the tire/wheel assembly. The operation of the device should further be capable of operational verification before the tire/wheel assemblies are released for control purposes and function without requiring an electromagnetic radiation shield.
An additional hurdle in the development of a suitable pressure measuring device for NASCAR or racing applications is that the tire employed in such applications is typically a dual tire system. The system uses an inner and outer tire, both seated at respective locations on a common rim. When properly seated the inner tire (which has higher inflation than the outer tire) pushes the beads of both tires against the rim flange. The inner tire has molded grooves to allow the inflation pressure in the outer chamber to reach the area adjacent to the flange between the two beads. The pressure measuring device is intended to measure the outer tire pressure and must be capable of accessing and measuring air pressure within the region between the inner and outer tires in a manner that does not interfere with tire performance or conflict with the accomplishment of the other objectives summarized above.
A further obstacle to achieving a satisfactory tire pressure measuring system is the need for such a system to communicate reliably with a remote receiver mounted on the vehicle. The tire pressure monitoring module may include a passive device that communicates with a remote receiver by means of RF signal. The RF signal from a passive device may not be strong enough to reach the receiver antenna mounted on the vehicle if subjected to interference from the tire rim. Accordingly, there is a need for a tire pressure monitoring system that allows for measurement of air pressure within one or more tires mounted on a rim while facilitating reliable communication of tire pressure data between the module and a receiver antenna mounted on the vehicle.